1. Field of the Invention
This invention relates to the oxidation of reducing gases. It is useful in converting unsaturated hydrocarbons to oxygenated petrochemicals, and in converting carbon monoxide (CO) to carbon dioxide (CO.sub.2). It is particularly useful in providing carbon monoxide (CO) detection systems and CO removal devices for use in automobiles, airplanes, industrial plants, mines, homes and other environments in which toxic or sub-toxic levels or carbon monoxide may be present. It also provides a superior filter for gas masks designed to remove CO.
2. Description of the Prior Art
The use of palladium chloride in hydrochloric acid solution to oxidize unsaturated hydrocarbons to oxygenated petrochemicals has been disclosed in Chemical Engineering News 39, No. 16, P52, 1961; Hydrocarbon Process. Petroleum Refiner 46, No. 11 135, 137, 203 (1967); Proc 6th World Petrol. Congr. Frankfurt/Maine 4, 461 (1963); and Hydrocarbon Process. Petrol. Refiner 42 No. 7 149 (1963). The use of palladium supported on a material resistant to hot acetic acid (e.g., carbon, alumina or silica) has been disclosed as a catalyst for converting unsaturated hydrocarbons to oxygenated petrochemicals. However, none of the prior art discloses a self-regenerating catalyst which uses a molybdate, tungstate, or vanadate with salts of copper, nickel, or iron in addition to palladium salts.
Several systems for the detection of CO in air have been deveoped. For example, U.S. Pat. No. 3,502,887 describes a CO detector constructed to resemble a cigarette lighter in the dashboard of an automobile. The presence of CO within the automobile is indicated by changes in the thermal conductivity of a sensing system which triggers warning lights or acoustical signals at a certain CO concentration. This instrument has not been widely used.
U.S. Pat. No. 3,245,917 discloses a CO indicator which includes palladium chloride and hydrochloric acid adsorbed on silica gel. On exposure to CO, this material turns black. German Pat. No. 1,113,596 discloses a CO indicator which is a mixture of silica gel, palladium chloride, and cupric chloride (CuCl.sub.2) or ammonium nitrate (NH.sub.4 NO.sub.3). In each of these two systems, exposure to CO reduces the palladium ion in the palladium chloride to palladium metal, which darkens the color of the indicator. On exposure to atmospheric oxygen, in the absence of any significant amount of CO, the palladium metal is slowly oxidized back to a simple palladium salt, e.g., PdCl.sub.2 or Pd(NO.sub.3).sub.2, requiring the presence of specific acid anions, i.e., Cl.sup.- or NO.sub.3.sup.-. These regeneration processes are slow, and the volatility of the acids involved leads to the loss of regenerating ability. Consequently, these CO detectors can be regenerated only a few times. Moreover, the sensitivity of these systems is too low to be useful for the detection of CO in the range of 10-100 parts per million (p.p.m.).
During World War II, the U.S. National Bureau of Standards developed a CO detection device for military use. It included a battery of glass tubes containing a silica gel impregnated with palladium and molybdenum salts. It is described in Analytical Chemistry, Vol. 19, No. 2, pages 77-81 (1947). The mixture on exposure to CO changes color from yellow to green or blue, depending on the concentration of CO. Due to its simplicity, specificity, sensitivity and reliability, this device was widely employed, particularly to detect dangerous concentrations of CO in the cabin atmosphere of aircraft. However, it can be used only once, which presents a serious disadvantage for continuous or quasi-continuous monitoring for CO because it requires the awkward and relatively expensive procedure of employing a battery of reagent columns in succession. This is impractical for most conditions of changing CO concentration in the atmosphere, e.g., in the cabin air of automobiles or aircraft under operating conditions.
This invention provides a new self-regenerating type of reagent reusable for an unlimited number of times so it not only can continuously monitor for CO, but can also be used to remove CO and other reducing gases (such as, hydrogen sulfide and unsaturated hydrocarbons) from ambient air or the combustion products of hydrocarbons. It can also be used to convert unsaturated hydrocarbons to oxygenated petrochemicals.